Mailing List Archive

Could someone kindly help explain the following paragraphs taken from the OpenStack TripleO documentation [1]?

"By default, Neutron is configured with an empty string for the Neutron external bridge mapping. This results in the physical interface being patched to br-int, rather than using br-ex directly (as in previous versions). This model allows for multiple floating IP networks, using either VLANs or multiple physical connections.

When using only one floating IP network on the native VLAN of a bridge, then you can optionally set the Neutron external bridge to e.g. “br-ex”. This results in the packets only having to traverse one bridge (instead of two), and may result in slightly lower CPU when passing traffic over the floating IP network."

Here I have difficulties to understand the traffic flow in the case of setting an empty string for the Neutron external bridge mapping (NeutronExternalNetworkBridge). My interpretation is that an empty string would map a physical interface directly to the br-int instead of the br-ex. Does it mean to bypass the br-ex and use the br-int for external traffics? If so, how come this would be less efficient as oppose to using br-int <-> br-ex <-> physical interface? This is where I got confused. Any helps would be greatly appreciated.